docs: def _validate_netconfig(self, conf):
          """
          Validate network configuration
  
          Args:
              conf(dict): spec
  
          Returns:
              None
  
  
          Raises:
              :exc:`~lago.utils.LagoInitException`: If a VM has more than
              one management network configured, or a network which is not
              management has DNS attributes, or a VM is configured with a
              none-existence NIC, or a VM has no management network.
          """
  
          nets = conf.get('nets', {})
          if len(nets) == 0:
              # TO-DO: add default networking if no network is configured
              raise LagoInitException('No networks configured.')
  
          no_mgmt_dns = [
              name for name, net in nets.iteritems()
              if net.get('management', None) is None and
              (net.get('main_dns') or net.get('dns_domain_name'))
          ]
          if len(no_mgmt_dns) > 0 and len(nets.keys()) > 1:
              raise LagoInitException(
                  (
                      'Networks: {0}, misconfigured, they '
                      'are not marked as management, but have '
                      'DNS attributes. DNS is supported '
                      'only in management networks.'
                  ).format(','.join(no_mgmt_dns))
              )
  
          for dom_name, dom_spec in conf['domains'].items():
              mgmts = []
              for nic in dom_spec['nics']:
                  net = self._get_net(conf, dom_name, nic)
                  if net.get('management', False) is True:
                      mgmts.append(nic['net'])
              if len(mgmts) == 0:
                  raise LagoInitException(
                      (
                          'VM {0} has no management network, '
                          'please connect it to '
                          'one.'
                      ).format(dom_name)
                  )
  
              if len(mgmts) > 1:
                  raise LagoInitException(
                      (
                          'VM {0} has more than one management '
                          'network: {1}. It should have exactly '
                          'one.'
                      ).format(dom_name, ','.join(mgmts))
                  )